In order to maximize efficiency under a limited radio resource in a wideband wireless communication system, methods for more effectively transmitting data in time, spatial, and frequency domains have been provided.
Orthogonal frequency division multiplexing (OFDM) uses a plurality of orthogonal subcarriers. Further, the OFDM uses an orthogonality between inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT). A transmitter transmits data by performing IFFT. A receiver restores original data by performing FFT on a received signal. The transmitter uses IFFT to combine the plurality of subcarriers, and the receiver uses FFT to split the plurality of subcarriers. According to the OFDM, complexity of the receiver can be reduced in a frequency selective fading environment of a broadband channel, and spectral efficiency can be increased when selective scheduling is performed in a frequency domain by using a channel characteristic which is different from one subcarrier to another. Orthogonal frequency division multiple access (OFDMA) is an OFDM-based multiple access scheme. According to the OFDMA, efficiency of radio resources can be increased by allocating different subcarriers to multiple users.
To maximize efficiency in the spatial domain, the OFDM/OFDMA-based system uses a multiple-antenna technique which is used as a suitable technique for high-speed multimedia data transmission by generating a plurality of time/frequency domains in the spatial domain. The OFDM/OFDMA-based system also uses a channel coding scheme for effective use of resources in the time domain, a scheduling scheme which uses a channel selective characteristic of a plurality of users, a hybrid automatic repeat request (HARQ) scheme suitable for packet data transmission, etc.
In order to implement various transmission or reception methods to achieve high-speed packet transmission, transmission of a control signal on the time, spatial, and frequency domains is an essential and indispensable factor. A channel for transmitting the control signal is referred to as a control channel. An uplink control signal may be various such as an acknowledgement (ACK)/negative-acknowledgement (NACK) signal as a response for downlink data transmission, a channel quality indicator (CQI) indicating downlink channel quality, a precoding matrix index (PMI), a rank indicator (RI), etc.
In general, a control channel uses more limited time/frequency resources than those used in a data channel. State information of a radio channel needs to be fed back in order to increase spectral efficiency of a system and a multi-user diversity gain. Therefore, effective design of the control channel is inevitable when large-sized data is fed back. In addition, the control channel has to be designed to have a good peak-to-average power ratio (PAPR)/cubic metric (CM) characteristic in order to reduce power consumed in a user equipment.
There is a need for a control channel structure capable of keeping good PAPR/CM characteristics while increasing transmission capacity.